Introduction: Non-vitamin K antagonist oral anticoagulants (NOAC) is the first line therapy to prevent ischemic stroke or systemic thromboembolism among atrial fibrillation (AF) patients. Since 2016, our study team enrolled patients under NOAC therapy in National Taiwan University Hospital, and measured their NOAC concentration to develop a cohort of NOAC treatment and NOAC concentration. Study purpose: Based on the cohort of NOAC therapy, we aim to investigate factors driving high or low NOAC concentration, and link NOAC concentration to clinical outcomes.

Methods: For all the participants in the cohort, we will retrieve their basic characteristic, concurrent medications, laboratory tests and clinical outcomes such as ischemic stroke, systemic thromboembolism, intracranial hemorrhage, major bleeding and death from the electronic medical records. The NOAC concentration will be compared to the expected range reported in clinical trials to define higher, within or lower than expected range. Univariate logistic regression will be used first, followed by multivariate logistic regression to investigate factors associated with high or low NOAC concentration. The relationship between NOAC concentration and clinical outcomes will be investigated by using the Cox proportional hazard model.